The present application is designed to delineate the behavioral and biological characteristics of a newly proposed eating disorder-the night eating syndrome-and to explore the neuro-endocrine mechanisms underlying its clinical characteristics. It was recently shown that persons selected on the basis of reports of morning anorexia, evening hyperphagia and insomnia manifest a distinct clinical entity, characterized by greatly increased food intake late in the day and evening, a lowered mood that falls during the afternoon and evening and frequent nighttime awakenings during which small, high carbohydrate snacks are consumed. Study of a different group of night eaters showed elevated cortisol levels throughout the 24 hours and attenuation in the nighttime rise in melatonin and leptin. This application is designed to more clearly delineate the syndrome by replicating and extending a previous study, this time using the same subjects for the behavioral and neuroendocrine measurements. The study will involve two phases. Phase I will consist of a 1-week outpatient study to determine the distinctive behavioral features of the night eating syndrome by comparing 30 night eaters with 30 persons suffering from binge eating and 30 persons without an eating disorder. During the week subjects will keep careful records of all food and fluid intake, and will wear sensitive motion sensors which record all nighttime awakenings. Phase II will consist of a 3-day hospitalization in the Clinical Research Center of the Hospital of the University of Pennsylvania comparing 15 night eaters with 15 non-eating-disordered controls. Polysomnography will determine the sleep architecture of the three groups, particularly the sleep stage during which arousals occur in the night eaters. Levels of melatonin, leptin and cortisol will be determined every 30 minutes, allowing far greater precision in determining circadian rhythms, than was possible with the 2-hour interval in our previous study. Statistical analyses will compare the results of the behavioral, sleep and neuro-endocrine studies with a goal to have the most complete characterization of an eating disorder yet undertaken. Exploratory analyses will include correlation among the behavioral variables (food intake, mood, and nighttime awakenings) and the neuro-endocrine variables to explore determinants of the clinical picture.